This application is a continuation-in-part of and incorporates by reference U.S. Ser. No. 07/319,994 filed Mar. 7, 1989, now issued as U.S. Pat. No. 5,040,199, which in turn is a continuation-in-part of U.S. Ser. No. 07/078,419 filed Jul. 27, 1987, now issued as U.S. Pat. No. 4,811,373, which in turn is a continuation-in-part of U.S. Ser. No. 06/885,098 filed Jul. 14, 1986, now issued as U.S. Pat. No. 4,947,414.
This invention relates to x-ray analysis apparatus.
In one important type of x-ray analysis apparatus, radiation is used to measure the density and distribution of bone in the human body. This procedure is helpful in diagnosing bone disease such as osteoporosis. Since this diagnostic technique uses potentially harmful ionizing radiation, bone densitometers are typically constructed to minimize the radiation exposure by minimizing the duration of radiation exposure while at the same time using the lowest intensity of the radiation possible.
In general, in a bone densitometer, a patient is placed on a table while a radiation source passes radiation through the patient. A detector is positioned on the opposite side of the patient from the source to detect the unattenuated radiation. Both x-ray tubes and radioisotopes have been used as a source of x-ray radiation. In each case, the radiation from the source is collimated to a specific beam shape prior to reaching the patient. This collimation reduces the exposure of the patient to the predetermined region of the patient opposite which are located the detectors. Various x-ray beam shapes have been used in practice and include fan beam, pencil beam, and cone beam shapes.
The shape of the beam and the shape of the detector system correspond. The detector in a fan beam system is a linear array of detectors. The actual detectors which make up the array range from low cost silicon photodiodes coupled with a scintillation material for use with higher intensity radiation to higher cost photomultiplier tubes coupled with scintillation material for use with low intensity radiation. 0 Since in bone densitometry the intent is to reduce the radiation exposure to the patient and since only a small percentage of x-rays penetrate the patient, highly sensitive photomultiplier tubes with scintillation crystals are useful. Such photomultiplier detectors are expensive, those of lowest cost being relatively large and therefore of relatively low inherent resolution.